system for detection of pathogens

Question 1

what is NAME

Answer 1

provides us with opportunities to define boundaries

up to the test system to define these boundaries and provide a measure that informs us

Question 2

mycobacterial genus

Answer 2

147 current species

only three are obligate human pathogens

M.tuberculosis
M.leprae
M.ulcerans

Question 3

how do we define a pathogen

Answer 3

commensal non pathogen (in host) = present but not capable of causing disease in host

e.g E.coli

zoonotic non pathogen (in carrier) = present but only in capable of causing disease in another host e.g E.coli

commensal opportunist (in host) = present and capable of causing disease in host but only in certain circumstances

e.g bactericides fragilis and coagulase negative staphylococcus

Question 4

are all positive samples diagnostic of disease

Answer 4

tuberculosis = 30% humans are infected, 18% have latent disease

helicobacter pylori = 50% humans infected, 25% have latent disease

Question 5

define pathogen

Answer 5

microbe capable of causing specific degree of host damage

Question 6

a test result is only as good as the sample provided

Answer 6

Sterile sites must be free from contamination
eg. Skin flora in blood cultures
Non sterile sites require decontamination of normal flora eg Faeces, Mouth, Skin
Samples with high volume or relatively low infected pathogen load require concentration (centrifugation, filtering)
eg CSF, Ascites, 24 hr Urine

Question 7

preparation phase and identification phase of culturing

Answer 7

culture:
prep phase = enrichment, purification, amplification

direct:
prep phase = concentration and sample treatment

identification phase:
molecular dna/rna
gross morphology
chemical composition

Question 8

direct light microscopy of samples

Answer 8

trichomonas vaginalis = 160million people infected

schistosoma mansonii = 83 mill people infected

entamoeba histolytica = 50 mill people

strongyloides = threadworm = 50% in UK children

Question 9

direct electron microscopy of samples

Answer 9

rotavirus from faeces
rabies from brain tissue
hepatitis B from liver
tonsilitis from nasal secretion

Question 10

immunofluorescent staining with pathogen specific conjugated antibody

Answer 10

treponema pallidum in gastric syphilis

measles virus infected into lab

vero cell line then stained with fluorescent antibody

Question 11

advantages and disadvantages of microscopy

Answer 11

advantages:
easy to perform 
rapid screening
some parasites have specific morphology 
specific immunofluorescence staining possible 

disadvantages
not sensitive
screening sputum smears require at least 10,000 orgs per ml to be visualised
general stains not specific
labour intensive
requires specialist interpretive expertise

Question 12

media types

Answer 12

non selective = blood agar

semi selective = macConkey agar, DCA, CLED

selective growth temperatures = campylobacter species

Question 13

describe selective media

Answer 13

non lactose fermenting
enterobacteria growing on cysteine lactose electrolyte deficient agar
from urine sample

DCA = selective for shigella and salmonella on faecal sample

Question 14

selective atmosphere

Answer 14

aerobic culture
s.aureus
catalase positive
e.coli

Question 15

respiratory pathogens

Answer 15

meningitidis
gonorrhorhea
influenzae
brucella melitensis

Question 16

anaerobic culture

Answer 16

clostridium tetani
clostridium botuniluum
costridium difficile
bactericides fragilis

C lo s tr id iu m p e r f r in g e n s o n B lo o d a g a r GrowninANAEROBIC atmosphere
Aerotolerant anaerobe producing spores in environmental conditions and exotoxins in humans causing Food poisoning and
Gas gangrene

Question 17

selective temp and atmosphere

Answer 17

campylobacter
42 degrees
10% CO2

Question 18

bacteriology environment

Answer 18

o2 = e.coli
co2= influenza
ANO2 = clostridium perfringens